In a conventional computer system, a CRT display apparatus is used as a standard monitor display. Due to the large consumption of power by a CRT display, the computer system, e.g., enters a power saving mode and de-energizes a CRT of the monitor display apparatus (which consumes most of the electric power) when there has been no operation input for a predetermined period of time, thus setting a standby state.
However, the operation control of the power saving mode is limited to a CRT display apparatus, but is not done for other types of display apparatuses. Even apparatuses other than the CRT require power savings. Furthermore, as for a normal television broadcast display, the user may leave home or fall asleep without turning off its power switch, and if the display can enter the power saving mode in such case, it is very convenient for the user.